The present invention relates to a process for forming a plating layer over the surface of an article of a synthetic resin, above all casting tools such as patterns and cores or core boxes, more particularly to a process for forming a solid plating layer over the surface of the synthetic resin article through the medium of a fine metal group thickly planted (or embedded) over the outermost layer thereof.
Synthetic resins have recently advanced into the field of metals remarkably because of their characteristics such as light weight, toughness, low cost and so on. Epoxy resin is, in particular, widely used as casting or molding tools, having replaced cast iron and aluminum, since the durability, resistance against rough handling and/or against abrasion by sand thereof have long been recognized. It still can not be said, however, that it is perfect in this use regardless of its biggest strong point, a relatively good resistance against abrasion as by sand; its durability, when used as patterns under severe conditions of high pressure molding and particularly as core boxes subjected to high abrasion, is far from being satisfactory. A further decisive defect resides in that it is far inferior to metal surfaces in the releasability or separability from the mold material for casting, such as molding sand.
Most known patterns made of epoxy resins for casting or molding are gel-coated over the outermost layer of a master pattern and the coating is retained by laminated layers of fiber impregnated with resins. It is next to impossible, however, to evenly or equally perform the gel-coating all over the master pattern surface of intricate shape, since some locally ungelled portions, exposed resin portions, may unavoidably occur.
Attempts at forming a durable plating layer over the surface of synthetic resins, especially of heat resisting ones, for example epoxy resin, have been made. None of them have been, however, successful. In metal plating over the surface of synthetic resins, unlike in intermetallic combinations where solid combinations can be observed, it is hard to expect solid combination between the base of the resin and the metal plated, where a mere physical clinging or sticking will occur that is weak in combining force. There is only one exception, that is ABS resin which barely can be said practicable due to the chemical etching applied thereon, while some other resins, such as polyethylene have been reported to be platable, however, it is no exaggeration to say that no practically successful metal plating processes on synthetic resins have yet been developed.